Cathode-ray tube beam-centering device



April 14, 1953 c. w. WANDREY CATHODE-RAY TUBE BEAM-CENTERING DEVICE Filed Oct. 4. 1950 Fig.1

POLE PIECE INVENTUR. CLARENCE WANDREY Patented Apr. 14, 1953 CATHODE-RAY TUBE BEAM-CENTERING DEVICE Clarence W. Wandrey, Wheaton, Ill., assignor to Zenith Radio Corporation, a. corporation of Illinois Application October 4, 1950, Serial No. 188,355

8 Claims. 1

This invention relates to centering devices for cathode-ray tubes to permit adjustment of the undeflected position of the electron beam developed therein.

Present-day cathode-ray tubes usually include a source of electrons situated in an elongated or neck portion of the envelope and a screen situated in an enlarged or bulbous portion thereof at the opposite extremity from the electron source. The cathode-ray tube also includes suitable elements for forming the electrons from the source into an electron beam and for directing the beam to impinge on the screen. There is also provided an electro-static or electro-magnetic arrangement for deflecting the beam in a predetermined fashion over a two-dimensional area of the screen so that image intelligence represented b a received television signal may be reproduced thereon. Furthermore, there usually is an electro-static, electro-magnetic, or a permanent magnetic arrangement for bringing the electron beam to a sharp focus so that the image intelligence may be reproduced on the screen clearly and distinctly.

It has been found very desirable to provide some means for centering or adjusting the undeflected position of the electron beam relative to the screen in order that the images may be reproduced correctly centered on the screen area despite slight misalignments of the various tube elements. One prior arrangement for accomplishing beam centering consists of a mounting structure for supporting a magnetic focusing device in a manner which permits the focusing arrangement to be physically displaced relative to the neck of the cathode-ray tube. The chief disadvantage of this arrangement is its inherent awkwardness, and the fact that it requires cumbersome and complicated structural apparatus to efiect displacement of the focusing device.

Another system for effecting a centering adjustment of the electron beam of an electro-magnetically deflected type of cathode-ray tube comprises control circuits for passing a controllable unidirectional current through the fieldand line-deflection windings. The amount of current traversing the respective deflection windings is adjusted until the electron beam is correctly centered on the screen. Accurate centering may be provided by this method, but it entails the need for extra and relatively expensive components and gives rise to an additional drain on the already overloaded power supply of the television receiver.

A further beam-centering arrangement has been proposed for cathode-ray tubes utilizing a permanent-magnet beam-focusing device. This latter type of focusing device usually comprises an annular permanent magnet which encircles the neck portion of the tube and establishes a magnetic focusing field therein. The annular magnet is provided with a pair of pole pieces mounted at its extremities and a magnet shunt between the pole pieces. Means are provided for adjusting the position of the shunt in an axial direction to vary the intensity of the field of the annular magnet within the cathode-ray tube and, thus, its focusing effect on the cathode-ray beam. A beam-centering adjustment is obtained by providing a metallic plate, mounted adjacent one of the pole pieces and movable transversely to the axis of the annular magnet to adjust the direction of the magnetic field to a position wherein the cathode-ray beam is properly aligned.

The present invention is concerned with a beam-centering arrangement of the last-mentioned type and provides a novel means for mounting the metallic plate to facilitate very accurate adjustment of the plate for beam-centering purposes.

It is, accordingly, an object of this invention to provide an improved adjustable magnetic structure for centering an electron beam in a cathoderay tube.

A further object of this invention is to providean improved cathode-ray tube beam-centeringstructure comprising a magnetic core member, and means for supporting a transversely-movable metallic plate at one end of the core and for imparting the required transverse motion to they plate in a simple and expedient manner.

in the appended claims.

which:

Figure 1 illustrates the beam-centering struc-- ture of the invention mounted on the neck section,

of cathode-ray tube, and,

Figure 2 shows a view of the beam-centeringstructure taken along the lines 22 of Figure 1..

Referring now to Figure 1, the cathode-ray tube illustrated therein is indicated by the nu-- meral l0 and comprises a neck section H and an. An electron, source i3 is mounted at one end of the neck secenlarged or bulbous section i2.

tion, and may take the form of any well-known type of electron gun for developing a cathode-ray beam within the tube and for directing the beam.

3 to impinge on a screen situated at the opposite end thereof.

The electron beam developed by source is is deflected over a two-dimensional area of the screen by means of a deflection yoke l5 mounted on neck I! adjacent the bulbous portion 12. The illustrated deflection yoke is of the electromagnetic type and is energized by lineand fielddeflection signals supplied thereto over leads [6 and I1 respectively. It is to be understood, however, that deflection yoke i5 may be replaced by suitable well-known electro-static deflection elements.

An annular core member or permanent magnet IB is mounted on neck portion H adjacent deflection yoke l5 and produces a magnetic field within the tube for focusing the cathode-ray beam. Core [8 has a pole piece l9 and a further pole piece 29 mounted at its extremities and held securely in position by means of studs 2| extending therebetween. Pole piece 20 also acts as a support for a metallic beam-centering plate 2 l, in a manner to be described. Magnetic core it is provided with an internal shunt 22 extending from pole piece 19 towards pole piece 29. Shunt 22 is threaded into pole piece [9 and its axial pesition may' be adjusted manually by means of a knurled portion 23. Adjustment of magnetic shunt 22 varies the gap between its extremity and pole piece 20 and, therefore, varies the flux distribution of magnetic core !8 and the intensity of the focusing field established within the cathode-ray tube. As is well known in the art, shunt 22 may be adjusted until the cathode-ray beam is brought into a sharp point focus on the screen It. As is also well known, shunt. 22 need not be internal as external shunts have been used to serve the same purpose.

As best shown in Figure 2, metallic plate 2% is provided with. a central aperture 25% through which the neck of the cathode-ray tube projects and is also provided with a pair of mutuallyperpendicular elongated slots 2", 26. The'slots are placed preferably at opposite extremities or extensions of plate 21'. Disc members 2?, 2-8 are disposed respectively within the slots and have diameters corresponding to the slot widths. The discs also have lip sections (Figure 1) overlapping the edges of the slots to support plate 2: securely against'pole piece 29.

A pair of control shafts 32 are rotatably mounted on pole piece 28 to support and actuate disc members 27, 28 which are eccentrically fixed thereto. Pole piece 2% includes a guide slot 33 into which a bent-over portion of metallic plate 2! projects.

The edges of each of the slots 25 and 26 form a pair of displaced, parallel, cam-engaging surfaces. Rotation of disc 2'! by control shaft 3! causes the disc to cooperate with the cam-engaging surfaces of slot 25 and shift metallic plate 2! transversely to the axis of core I8, and in a vertical direction relative to pole piecezc. Likewise, rotation of disc 2-8 by control shaft 32 causes the disc to cooperate with the cam-engaging surfaces of slot 2% and shift metallic plate 2% transversely to the core axis and in a horizontal direction relative to pole piece 2d. Thus, by rotation of control shafts 3i and 32-, the direction of the magnetic field developed. by core is within the cathode-ray tube may be altered to accomplish centering of the cathoderay beam developedtherein.

The invention provides, therefore, an improved beam-centering device in which the beam-ceritering plate may be supported on the magnetic core and moved in two distinct directions transverse to the axis of the core by an extremely simple mechanism. The structure does not require retaining rings, resilient members, or the like, for the beam-centering plate 2 i. This plate is supported on the core and transverse motion is imparted thereto by the facile expedient of a pair of discs eccentrically mounted on control shafts Si, 32.

Although a particular embodiment of the invention has been shown and described, modifications may be made. For example, slots 25 and 26 need not be disposed at opposite extremities of centering plate 2!, but may be spaced around the periphery of the plate. Moreover, the cam engaging surfaces of the discs need not be formed by slots but may take the form of tracks on the centering plate. Therefore, it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

I claim:

1. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: a magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic plate for cooperating with said core member to determine the position of said electron beam, said plate, being supported at one end of said core member having an aperture through which said neck section projects, and further having first and second pairs of displaced parallel camengaging surfaces associated therewith; a first ccentrically-mounted disc member supported between said first pair of cam-engaging surfaces and having a diameter corresponding to said displacement of said first pair of surfaces; a second eccentrically-mounted disc member supported between said second pair of cam engaging surfaces and having a diameter corresponding to said displacement of said second pair of surfaces; and control means for selectively actuating said disc members to impart motion to said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

2. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: a magnetic core member constructed to encircle a neck section of cathode-ray tube for developing a magnetic field therein; a metallic plate for cooperating with said core member to determine the position ofsaid electron beam, said plate being supported at one end of said core member, having an aperture through which said neck section projects, and further having first and second mutually-perpendicular pairs of displaced parallel cam-engaging surfaces associated therewith; a first eccentrically-mounted disc member supported between said first pair of cam engaging surfaces and having a diameter corresponding' to said displacement of said first pair of surfaces; a second eccentrically-mounted disc member supported between said second pair of cam-engaging surfaces and having a diameter corresponding to said displacement of said second pair of surfaces; and control means for se lectively actuating said disc members to impart motion'to-said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

3. A magnetic structure for centering an elecfirst and second mutually-perpendicular pairs of displaced parallel cam-engaging surfaces at opposite extremities thereof; a first eccentricallymounted disc member supported between said first pair of cam-engaging surfaces and having a diameter corresponding to said displacement of said first pair of surfaces; a second eccentrically-mounted disc member supported between said second pair of cam-engaging surfaces and having a diameter corresponding to said displacement of said second pair of surfaces; and control means for selectively actuating said disc members to impart motion to said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

4. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: a magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic plate for cooperating with said core member to determine the position of said electron beam, said plate being supported at one end of said core member, having an aperture through which said neck section projects, and further having a pair of slots therein or preselected widths; a pair of eccentrically-mounted disc members respectively supported within said slots and having diameters corresponding to said preselected width thereof; and control means for selectively actuating said disc members to impart motion to said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

5. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: a magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic plate for cooperating with said core member to determine the position of said electron beam, said plate being supported at one end of said core member, having an aperture through which said neck section projects, and further having a mutually-perpendicular pair of slots therein of preselected widths and disposed at opposite extremities thereof a pair of eccentrically-mounted disc members respectively supported within said slots and having diameters corresponding to said preselected width thereof; and control means for selectively actuating said disc members to impart motion to said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

6. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: a magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic plate for cooperating with said core member to determine the position of said electron beam, said plate being supported at one end of said core member, having an aperture through which said neck section projects, and further having a pair of mutually-perpendicular slots therein of preselected widths and disposed at opposite extremities thereof; a pair of disc members respectively disposed within said slots and having diameters corresponding to said preselected widths thereof; and a pair of control shafts rotatably supported on said core and eccentrically coupled to said respective discs to rotate selectively said discs and impart motion to said plate in two distinct directions transverse to the axis of said core for effectively varying the position of said electron beam.

7. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: an annular magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic supporting plate mounted at one end of said core member and having an aperture through which said neck section projects; an annular plate for cooperating with said core member to determine the position of said electron beam constructed to encircle said neck section and having a pair of mutually-perpendicular slots therein of preselected Widths disposed at opposite extremities thereof; a pair of control shafts rotatably mounted on said supporting plate; and a pair of disc members having diameters corresponding to said preselected widths of said slots eccentrically mounted on said control shafts and disposed in said respective slots to maintain said annular plate in juxtaposition with said supporting plate; whereby selective rotation of said control shafts causes said discs to impart motion to said annular plate in two distinct directions transverse to the axis of said core to effectively vary the position of said electron beam.

8. A magnetic structure for centering an electron beam in a cathode-ray tube comprising: an annular magnetic core member constructed to encircle a neck section of said cathode-ray tube for developing a magnetic field therein; a metallic supporting plate mounted at one end of said core member and having an aperture through which said neck section projects; an annular plate for cooperating with said core member to determine the position of said electron beam constructed to encircle said neck section and having a pair of mutually perpendicular slots therein of preselected widths disposed at opposite extremities thereof; a pair of control shafts rotatably mounted on said supporting plate; and a pair of disc members eccentrically mounted on said control shafts and disposed within said respective slots, said discs having diameters corresponding to said preselected widths of said slots and outwardly extending lip sections overlapping said slots to maintain said annular plate in juxtaposition with. said supporting plate; whereby selective rotation of said control shafts causes said discs to impart motion to said annular plate in two distinct directions transverse to the axis of said core to effectively vary the position of said electron beam.

CLARENCE W. WANDREY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,431,077 Poch Nov. 18, 1947 

